U.S. Pat. Nos. 3,312,592; 3,910,930 and 3,914,238 disclose pharmacologically active 2-(2-amino-1-hydroxyethyl)-1,4-benzodioxans, which are obtained as mixtures of diastereoisomers, separable only by cumbersome methods. According to the present invention a stereospecific process is provided, yielding intermediates for said compounds in the pure erythro or threo forms, and requiring but simple, inexpensive starting materials. Moreover, said process is especially suited for the unambiguous preparation of ring-A-substituted 1,4-benzodioxans.